A large proportion of industrial injuries result from material handling and lifting tasks. Back injuries occur with great frequency, often cause acute suffering and serious disability in the workers involved, and are extremely costly to the industrial economy. The objectives of this research are: (1) to analyze the three-dimensional force systems that act in the human spine during industrial handling and lifting tasks; (2) to analyze the mechanical stresses within the intervertebral motion segments caused by these systems. Basic features of the program are: (1) the use of computer-generated analogs of the entire thoracolumbar spine and finite-element models of single intervertebral motion segments, and (2) the use of experimental data to ensure that the models are valid, and to confirm predictions made from model obtained results. The results of these studies should lead to significant improvements in understanding how the incidence and severity of industrial back injuries can be reduced.